Analyte-selective sensor

Details Analyte-selective sensor Analyte-selective sensor

1997-06-16

1999-12-21

Till, Terrence R.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204415, G01N 2712

Patent

active

06004442&

DESCRIPTION:

BRIEF SUMMARY
The invention relates to an analyte-selective sensor comprising an analyte-specific layer, which is so modified that ions or neutral species contained in solutions can come into contact with the layer, so that then an alteration in the electrical properties occurs.
In order to detect ions in solutions the potentiometric ion-selective electrode is widely used (Camann, K. Die Arbeit mit Ionenselektiven Elektroden, [Working with Ion-selective Electrodes], 2nd ed., Springer Verlag: Berlin, Heidelberg, N.Y., 1977)). Ion-selective electrodes are electrochemical sensors by means of which the concentration (more precisely the activity) of specific ions can be detected by means of a potential difference. The ion-selective potential difference occurs at the phase boundary between electrode material/electrolyte and, according to the Nernst equation, depends on the activity of a specific ion in the solution.
The necessity for a reference electrode is the decisive disadvantage in the use of potentiometric measurements for detecting ion activities in solution. Other than for resistance and capacity, the absolute values of the electrical potential have no physical meaning, as the potential can only be defined with respect to a reference value. In electrochemistry such a reference value is usually provided by the potential of the reference electrode.
The other basic restriction in potentiometric analysis methods relates to the composition of the ion-selective membrane. The requirements of the nature of the specific bond and/or of the complexing points within the membrane are to be set in such a way that the potential difference is selectively built up at the boundary surface membrane/solution in dependency on the presence of a specific species in the solution. For example, this bond should not be too strong, so that a sufficiently rapid exchange of the detected species between the membrane phase and the solution is possible.
Next to the potentiometric methods, the most frequently used electrochemical analytical methods are those which measure the current flow by means of an appropriately prepared or modified conductive or semiconductive collector electrode. The potential of this electrode is fixed by that of the reference electrode. The current flow measured results from the electrochemical redox reaction which takes place at the boundary surface between collector electrode/solution. In addition to this necessary reference electrode, the use of these measurement methods is also restricted by the fact that the species measured at the working potential applied to the collector electrode must be electroactive, and thus only a restricted number of analytes can be measured. Moreover this potential must be different from that of the interfering species. The latter frequently represents a problem, as many chemical or large groups of chemical compounds have very similar redox properties. On the other hand, the electrical potentials necessary for many compounds lie outwith the practicably usable range.
Among the non-electrochemical methods most used for specific recognition of charged and neutral species are the various types of liquid chromatography. In this case the sample to be analysed is brought into contact with a so-called stationary phase, e.g. a polymer layer, which specifically bonds or retains the detected species. The strength of this bond determines the retention time of the analyte within the chromatographic column. When tailor-made stationary phases are used, a large number of species can be identified. However, this type of analytical measuring arrangement is extremely complex and expensive.
The other important class of analytical methods for detecting charged and uncharged species in gaseous or liquid medium uses measurement of the resistance or capacitance. Alterations in the conductivity or of the dielectric properties of a layer of a sensitive material are indicated in dependency on the interactions with the detected species. Thus resistance and capacitative sensors are widely used in the field of detection of

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patent: 5200051 (1993-04-01), Cozette et al.
patent: 5337018 (1994-08-01), Yamagishi

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